Last year, 72 dams were turned from walls to waterways, either torn down or blown up in the United States to restore some 730 miles of rivers from California to Pennsylvania.

That set a new record in dam removals, according to conservation group American Rivers.

While a dam building boom continues in the Amazon, China, and Africa, the tide has turned in Europe and the U.S., where conservationists have been working to tear down decrepit and environmentally damaging dams over the past 20 years.

“The river restoration movement in our country is stronger than ever,” Bob Irvin, president of American Rivers said. “Communities nationwide are removing dams because they recognize that a healthy, free-flowing river is a tremendous asset.”

The map below shows where dams were removed in 2014.

The cost of keeping old dams intact often is too high. Besides saving money, returning rivers to their natural course improves water quality, revitalizes salmon runs, and promotes wildlife biodiversity.

Eighty-two percent of the 1,185 dams removed since 1912 have been taken out in the last two decades. While the focus has been on demolishing outdated dams that pose a risk to public safety, American Rivers and other conservation groups are moving to watershed-wide restoration by eliminating multiple dams along a river.

"We're trying to work more strategically, to have the biggest impact with limited funds and limited people," Serena McClain of American Rivers told National Geographic. "So we're looking not just at old and outdated dams, but at dams that currently serve a purpose."

One of the most spectacular dam demolitions was the dismantling of the 210-foot Glines Canyon Dam on Washington’s Elwha River—the largest ever removed in the United States.

That dam had been one in a line of hydroelectric dams stopping native salmon from swimming upstream to lay their eggs. But last year, habitat managers spotted chinook salmon in their historical spawning grounds for the first time in 100 years. It took nearly three years and $325 million to restore the river to its natural state.

These are the states that removed the most dams in 2014:

Pennsylvania: 17

California: 12

Michigan: 6

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